1. Field of the Invention
This invention relates to rotary drive apparatus in which a rotatable member is coupled by a cable to another rotatable member and, more particularly, to a rotary drive apparatus where one rotatable member is coupled by a cable to another rotatable member having an axis of rotation spaced apart from its geometric center.
2. Description of the Prior Art
U.S. Pat. No. 4,351,197 (Carson) discloses several embodiments of rotary drive systems in which a screw is coupled to a drum by a cable connection and in which rotation of the screw results in rotation of the driven member. The driven member in each embodiment is a drum rotating about its geometric center. Since the driven member rotates about its geometric center, the rotation of the driven member is linear. That is, for a predetermined rotation of the driving member, a corresponding rotation of the driven member will result, and the ratio of the rotation is, of course, dependent upon the ratio of the cable pitch radii of the driving and driven members.
In some applications of a rotary drive system, it may be advantageous to have a non-linear rotational output of the driven member. That is, for a predetermined rotation of the driving member, the rate of rotation and the angle rotated of the driven member may be variable, depending on the distance from the geometric center of the driven member to its axis of rotation. In such an eccentric rotational system, either the driven member or the driving member must be pivoted to allow the driven member to rotate asymmetrically. Accordingly, either the driving member or the driven member may be fixed and the other may be pivotally secured.